1. Field of the Invention
The invention relates to branched, amorphous, polyester-based macropolyols having a narrow molecular weight distribution and a process for making the macropolyol.
2. Description of the Related Art
Saturated polyester resins are known and are conventionally prepared by condensing saturated dicarboxylic acids, their anhydrides or other esterifiable derivatives with diols. Their properties depend largely on the nature and proportion of the starting materials.
Branched, polyester-based macropolyols are described, for example, in DE 196 49 394. These materials are prepared from a defined selection of raw materials and have relatively high OH numbers of from 80 to 300 mg KOH/g, and acid numbers of from 5 to 30 mg KOH/g.
Polyester molecules with high OH numbers and high acid numbers may not possess the functionality and/or high molecular weight desirable in polymer resins. One resulting disadvantage is that a higher proportion of crosslinker is needed and higher costs may result when isocyanates are used as crosslinker molecules. High acid number may also have other disadvantageous consequences since as a result of the hydrophilic centers (carboxyl groups) the water resistance of, for example, coatings, can be adversely affected.
US 2002026028 discloses polyesterpolyols having a similar structure with similar disadvantages.